The Optical Properties of Bragg Fiber With a Fiber Core of 2-Dimension Elliptical-Hole Photonic Crystal Structure

The optical properties of birefringent Bragg flber with a flber core of 2-dimension (2D) elliptical-hole photonic crystal structure has been studied. Elliptical air holes are introduced into the flber core to form a normal 2D photonic crystal structure with a hole pitch (center-to-center distance between the air holes) much smaller than the operation wavelength of the Bragg flber. The elliptical-hole photonic crystal structure acts as an anisotropic medium with difierent efiective indices for transmission light of difierent polarization, which inevitably results in high birefringence (up to the order of magnitude of 0.01) of the Bragg flber. The proposed Bragg flber possesses difierent band- gaps for difierently polarized mode. Besides the periodic alternating layers of high/low refractive indices, the bandwidth of the band-gap is also dependent on the efiective index of the flber core, which can be controlled by the area of the elliptical air holes.